Double Decks choose m cards from 2 decks of n cards 1+e+”-∑（因e+ 90)-200 -区：￾ ￾￾k ￾k ￾ ￾ x￾ Double Decks 2 deck of s n cards choose m cards from (1 + x + x2) n = ￾ k ￾n k ￾ (x + x2) k = ￾ k ￾n k ￾ xk = ￾ k ￾ ￾￾k ￾n k ￾￾k ￾ ￾ xk+￾ = ￾ m ￾￾ ￾ ￾ n m ￾ ￾ ￾￾m ￾ ￾ ￾ ￾￾ xm ( )